Method of forming batts of silica fibers



April 21, 1953 L. PARKER METHOD OF FORMING BATTS OF SILICA FIBERS FiledDec. 19, 1949 mw om u2 Jal mh w c F Kurt;

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the practice as Patented pr. 21, 19553 METHOD OF FORMING BATTS OF SILICAFIBERS Leon Parker, Burbank, Calif., assignor to The H. I. ThompsonCompany, Los Angeles, Calif., a corporation of California ApplicationDecember 19, 1949, Serial No. 133,896

- 8 Claims'.

leached to remove the non-siliceous oxides and thus produce fibers ofhigh silica content, the

silica lcontent depending upon the degree of extraction of the bers.Depending upon the composition of the fibers, these non-siliceous oxidesmay be extracted either by plain w-ater or with While glass iibers ofVarious compositions may be so extracted .by both neutral water and acidWater, the boro-silicate glasses Which are usually employed in formingglass filaments for Weaving into textile materials which have less than'70% silica content may be extracted without previorus preheating of theglass struc- Such iilaments may be leached without such heat treatmentand since they are usually of less than .001" in diameter, they may beleached to remove the acid soluble oxides other than silica Withoutdestruction of the fiber. The

vglasses which lend themselves best to drawing readily leached with acidto remove the metal oxides other than silica.

The resultant product contains some water of hydration in theneighborhood of about 8% to 11%y and may be dehydrated by heating totemperatures of about 1000 F., preferably in the `region of about 1400to 1600o F. By proper control of the acid extraction process theresultant fibers after iiring contain high silica fcontent and may be ashigh as 90% and even 'substantially 99.9% of silica as determined byYthe hydronuoric acid method. v

" ATheabove process uand the eiect of the glass composition and degreesof treatment in producing such extracted glass ibers are describedrin'the Parker and Cole application, Serial No. 6I-59,098, filed May 11,1946, now Patent No. 12,491,761 and United States Patent No. 2,461,841

issued to Nordberg, to which reference may be One of the most usefulapplications of the Labove process is in the manufacture of battsl ofsilica fibers. .Such batts have found particu- ;larly useful applicationas insulating blankets.

In producing the batts for this use it has been described in theaforesaid Parker- Cole application to form the silica fiber batts by@leaching batts of. elongated glassY berslwhich [are cemented togetherby 'means of resin..V This been necessary` sincey where employing un-`for the felting of cellulose or other fibers.

2 bonded glass fiber batts, the batts become wadded up in the leachingsolution. The resin bonded batts, however, keep their shape duringleaching and the resin does not materially interfere with the leachingoperation.

A number o f difliculties are present Vin the above procedure. Thus, thebatts :are formed of long glass fibers and are costly since theelongated glass iibers are costly. The bers must be bonded by resin,introducing an additional item of cost. Because of the presence of resinin the glass ber batt, special precautions must be provided to preventsegregation of resin yduring leaching. As is disclosed in Parker andYZack application, Serial No. 34,354 filed June 21,

1948, now Patent No. 2,500,092, it has been discovered that the ends ofthe rolls of glass liber batts leached in the acid become black andbrittle on ring. Thus, these ends must be cut off, resulting in a lossof as much as 25% of the cost of the leached and red batt. Thisdifficulty is corrected in the cited application by rolling the glassfiber batt inside a porous acid resistant blanket.

The process is a. batch process, the Wrapped blankets are immersed inacid and leached, then removed and introduced into a washing machine andthen dried. The batts :are unrolled Vand re-rolled for firing.

I have now devised asimplified procedure which is more expeditious, moreeconomical, omits several of the above steps, and may be employed in acontinuous manner. In my present intakes it possible to employ scrapfibers which are of the order of less than about 1 inch in length.Because I pulp the fibers in the vacid I avoid the resin bonding step ofthe present commercial practice.

The pulped and extracted fibers may then be formed into a' blanket andWashed by Various procedures. Thus, they may be iiltered either on aplate or rotary iilter to form a filter cake, or

formed into a felt by means similar to those used A batt of short fibersis thus produced.

'I have `found that the felted fibers formedby the ltering operation aresufliciently strong, even when wet, to be rolled or otherwise handled inthe ring operation.

By this procedure I also avoid the wrapping operation referred to aboveand get clean white fired batts of silica with no loss other than theloss due to leaching out of thenon-siliceous oxides and the shrinkage ofthe bers on dehydration. The ring operation causes a shrinkage of theleached batt and an Yinterlocking of the leached fired bers andincreases the mechanical strength of the batt.

The process will be furtherdescribedbyreierence to the drawing, whichshows a schematic flow sheet of the process.

The bers are stored in st oragechamber I from which they are fed, ifthey are too long, through the chopper to be cut into fibers of suitablelength. If they are of suitable length they maybe fed directly totheleaching apparatus. Experience `has shown that it is preferable toemployglass i'lbersgreater than la in length, since the batts producedfrom such bers are structurally weak. On theother hand, bers of 2 orVmore in length are diicult tokeep in suspension. It has been found thatfibers of from 1/24 to l'f in length are Vmost usefully employed. Theymay be readily pulped and stay in suspension adequately and form battsof adequate strength. The fibers of such length are fed into theleaching tank 3.

. The feeding of the bers from the chamber I through the cutter 2 andinto the leachingV charn- .deck Classifler, `a submerged spiral type ofclassifier, as Akins Washing Classiersuch as, for example, described inPerry Chemical Engineers Handbook, pages, 1320, etc. 1934 ed).

. The leaching solution depends upon the type of glass employed in themaking of the bers as indicated above.v

I prefer to employ the acid leachable glass bers referred to above andto employ as acid those acids whose salts ofthe non-siliceousmetallicoxides are soluble Ain the acid solution. Such acids may be HC1, HNOa,ti'ichlor, acetic acid, or acetic acid. l have `found H Clto be aparticularlruseful acidv ,for thisrurpose.- .,'lhe portions oftheapparatusin contactwthth@ acid are made iacid resistant by conventionalprocedures..k The use of a multistage hydraulicclassiiier as a leachingapparatus is illustrated schematically. `Storage tank 4 contains HC1acid of strengthof f rom about 5 to about 15%. The acid is fed through aheater 5 Y whererit is heated to aterriperature of f rommlOtlo F.1uptcboiling; temperatures ofabout 140 to 180 F. are particularly .ilflil.The id flowinsihelgh the leffher. 3 is cuntercurrent to the passage ofthe c ut bers and the spent acid overows through line `Ii. The

time of contact in the leaching chamber may be from 6 minutes to 2hours, depending on the str ength of the acid formed and the degree ofwhere it may be neutralized with lime and discharged to the sewer.

'I'he washed fibers are separated as a thick slurry from the bulk of theacid and conveyed Ai 1 i to the washingsystem I 5 of design similar to3. Water, for example, distilled water, from storage .I6 maybe used towash the iibers substantially freeof chlorides.

The Washed nbers are introduced into pulping tank I9 where the fibersare agitated and dispersed by agitator 20 in the presence of water addedthrough 2 I The pulp is discharged through line '2| by pump 22 onto atravelling porous belt such as is used in felting oi fibrous materialsuch as paper. The'belt, for example, is operated by means of pulleys 23and 23 actuated by suitable machinery. Such apparatus is conventional inthe paper making and felting arts. The belt travelsover a vacuum chamber24 and the excess water is sucked into the vacuum chamber 24 and thewater pumpedby pump 25 and line 26 into the water storage I6.

The felted fibers are in the form of a batt and are fed olf the belt 22via 'guide 21 onto the belt -28 operated by pulleys 29`and 39 to passthrough a conventional tunnel drer.3 I operated in conjunction with asuction fan 32 and suitable source of heat as `is usual in tunnel driers.

The dried batt is then` passed over guide 33 onto the travelling belt 34operated by pulleys. The belt may be made up of Woven silica b'ers or beva metallic belt made of material which ls dimensionally stable attemperaturesof about 1500 to 2000 F. Thebatt passing with belt 34through the furnace 3`Iv is exposed to the vflames from burners 38 andheated to fa temperaturefof 1500-2000 F. to dehydr'ate and shrink the'fibers The shrinkage of the bers onh'a'ting improves the interlockbetween the be'rs in the batt.

The red batt is fed oif belt 34 to belt 3 9 via guide 40 and isair-cooled during passage of the belt driven pulleys 4I and 42. 'I hecooled 'batt Vis fed ofi the end f the belt'39 and wound into 1o11s4a.

VWhile'I have described a'partcular embodiment of my invention for thepurpose 'of illus'- rration it should oo understood that variousmodcatioris and 'adaptations thereof may'lbe made Within the spirit of"the invention as'v'set forth' in the appended clai'ns.

1. A method of forming shrunk barns of interlaced shrunk silica fibersof 'short length, which comprises suspending short lengths of individual'glass bers' in a vleaching solution to vextract'ncnslliceous'glasseform'ing oxide vfrom the -glassfand extra-ct the Ynon-'siliceousglassforminx "oxides from said glass bers, producing a suspension ofhydrated silica bers in said leaching solution, separating said hydratedsilica fibers from said leaching solution, subsequently washing andfiltering said hydrated silica fibers to produce a batt of interlacedshort hydrated silica bers. heating said batt to an elevated temperatureto dehydrate said fibers and shrink said silica fibers and said batt.

3. A method of forming shrunk batts of interlaced silica bers of shortlength, which comprises suspending glass bers in a leaching solution toextract the non-siliceous glass-forming oxides from said glass fibers,producing a suspension of hydrated silica fibers substantially free ofsaid non-siliceous metallic oxides in said leaching solution, removingsaid leaching solution from the hydrated silica fibers, subsequentlyWashing said fibers with Water and forming a suspension of said hydratedsilica bers in the water, separating the Water from said hydrated fibersto form a batt of interlaced hydrated silica bers, heating said batt todehydrate said bers `and to shrink said batt.

4. A method of forming shrunk batts of interlaced silica 'bers of shortlength, which comprises suspending short lengths of glass fibers in anacid solution said acid being chosen from the group consisting ofhydrochloric acid, nitric acid, acetic and trichloracetic acid, to leachfrom the suspended glass fibers a major portion `of the non-siliceousglass-forming oxides of said glass, and to form a suspension of hydratedsilica bers in said acid, separating the acid solution containing thedissolved material from the hydrated silica fibers, Water Washing theseparated fibers substantially free of acid, forming a suspension ofsaid washed fibers in water, filtering said suspension to form a batt ofhydrated silica bers of short length, subsequently heating said batt toan elevated temperature, todehydrate and shrink said fibers and saidbatt.

5. A method of forming shrunk batts of interlaced silica iibers of shortlength, which comprises suspending said fibers in dilute hydrochloricacid solution to extract the non-siliceous metallic oxides from theglass, forming short bers of hydrated silica substantially free ofnon-siliceous metallic oxides suspended in spent hydrochloric acidcontaining chlorides, separating the spent acid from said hydratedsilica fibers, washing the fibers substantially free of chlorides.forming a suspension of said washed hydrated short length fibers inwater, separating the water from said bers to form a batt of interlacedshort length hydrated silica bers. heating said batt to an elevatedtemperature to dehydrate said bers and to shrink said batt.

6. A method of forming felts of silica fibers which comprises leachingglass fibers with a leaching solution to extract the non-siliceous glassforming oxides from the glass and to form hydrated silica bers, andltering a suspension of said hydrated silica bers to form a felt of saidhydrated silica bers.

7. A method of forming felts of silica bers which comprises suspendingglass fibers in a leaching solution to extract non-siliceousglassforming oxides from the glass and to form hydrated silica bers,separating the leaching solution from the silica fibers, forming anaqueous suspension of said hydrated silica bers, and felting thehydrated silica bers from said aqueous suspension.

8. A method of forming felts of silica fibers which comprises leachingglass fibers with a leaching solution to extract non-siliceousglassforming oxides from the glass and to form hydrated silica bers,ltering a suspension of said hydrated silica fibers to form a felt ofsaid hydrated silica bers, heating said felt to an elevated temperatureto dehydrate and shrink said felt.

LEON PARKER.

References Cited in the le 0f this patent UNITED STATES PATENTS NumberName Date 2,217,005 Clapp Oct. 8, 1940 2,286,275 Hood et al. June 16,1942 2,338,463 Skaupy et al Jan. 4, 1944 2,459,803 Francis, Jr J an. 25,1949 2,461,841 Nordberg Feb. 15, 1949 2,483,405 Francis, Jr. Oct. 4,1949 2,500,092 Parker et al Mar. 7, 1950 2,504,744 Sproull etal Apr. 18,1950 FOREIGN PATENTS Number Country Date 37,900 Germany Dec. 2, 1886113,887 Australia June 24, 1940 OTHER REFERENCES J. Franklin Inst., pg.457, June 1946.

6. A METHOD OF FORMING FELTS OF SILICA FIBERS WHICH COMPRISES LEACHINGGLASS FIBERS WITH A LEACHING SOLUTION TO EXTRACT THE NON-SILICEOUS GLASSFORMING OXIDES FROM THE GLASS AND TO FORM HYDRATED SILICA FIBERS, ANFILTERING A SUSPENSION OF SAID HYDRATED SILICA FIBERS TO FORM A FELT OFSAID HYDRATED SILICA FIBERS.